The present invention relates generally to a multiplexes/demultiplexer and, more specifically, to a modular multiplexes/demultiplexer for use with backplane systems.
Multiplexing and demultiplexing are well known concepts in tele- and data-communications. In optics, one form of multiplexing involves combining various channels of varying wavelengths on a single fiber. This way, the number of fibers needed for linking distant locations is miinimized. Conversely, one form of demultiplexing involves splitting channels propagating on a single fiber onto discrete fibers. Demultiplexing is generally required, for example, to switch, route or otherwise manipulate individual channels.
To effect multiplexing/demultiplexing, often xe2x80x9ccascadedxe2x80x9d add/drop filters are used, a simplistic arrangement of which is shown in FIG. 5. The add/drop filter 51 is a well-known optical component which, in one direction, couples or xe2x80x9caddsxe2x80x9d channels propagating on two or more input fibers 52a, 52b onto a fewer number of output fibers 53, and, in the other direct, splits or xe2x80x9cdropsxe2x80x9d channels propagating on a fiber 53 onto two or more fibers 52a, 52b. The add/drop filters are typically tuned to add/drop different wavelengths according to ITU grid. The ITU grid is well known and thus is not specifically addressed herein. It should be understood that add/drops filters for multiplexing and demultiplexing are generally the same; it is only the direction in which the light is propagating that determines whether the add/drop filter serves to add or drop channels. Therefore, for simplicity, the discussion herein will focus on multiplexing, but the concepts discussed apply equally as well to demultiplexing.
To achieve a high degree of multiplexing, that is, one in which many channels are combined on a single fiber, it is necessary to cascade the add/drop filters together. In this arrangement, the output fiber 53 of the add/drop filter 51 (i.e., the single fiber carrying the channels of the input fibers 52a, 52b) is used as one of the input fibers 55a of another add/drop filter 56. Thus, the channels carried on the output fiber 53 of the add/drop filter 51 are combined with the channels of the other input fibers) 55b of the other add/drop filter 56. This xe2x80x9ccascadingxe2x80x9d configuration may be repeated with other add/drop filters downstream and, in this way, combine many channels onto a single fiber 57. For example, as shown in FIG. 5, 8 channel multiplexing can be achieved as follows: 4 add/drop filters are used first to combine 8 channels onto 4 different fibers; then 2 add/drop filters are used to combine the channels onto 2 fibers; and finally, a single add/drop is used to combine the channels onto the single fiber 57. The cascading arrangement in FIG. 5 is particularly simplistic and was used for illustrative purposes. Most configurations used in industry tend to be more complex to minimize reflective losses or otherwise optimize the performance of the add/drop filers. The number of channels that may be carried on a single fiber is limited by many factors which will not be addressed specifically herein.
From the above description and FIG. 5, it becomes apparent that the arrangement of cascaded add/drop filters and the ganglia of interlinking fibers needed to effect a high degree of multiplexing can become complex and physically difficult to manage, especially when there is a need to maintain a minimum bend radius on all the fibers. This difficulty is complicated by recent trends in the industry that require more compactness and modularity. Specifically, there is a premium on space in many of because the optical devices in which optical multiplexers/demultiplexers are used, such as in routers and switches, since these devices are need. Furthermore, as in most industrial products, there is a desire to modularize the components to facilitate scaling up as multiplexing needs require, e.g., from 8 channels to 16, and from 16 to 32 and so on. Furthermore, modularization reduces the number of different parts that must be stocked or otherwise accounted from when designing the optical devices.
At the heart of modularization is packaging. A modular add/drop needs to be contained preferably in a single housing and this housing needs to be compact and robust. These requirements coupled with complexity inherent in cascading add/drop filters, especially with the minimum fiber bend radius requirements of the individual fibers, pose a significant challenge. The present invention meets this challenge.
The present invention overcomes the problems presented in modularizing an add/drop by arranging the add/drop filters in submodules. This way, the surface area available to assemble all the add/drops filters and manage their fibers is effectively increased. Additionally, by using a tray having submodules, one submodule can be designated as the add submodule and the other submodule can be designated as the drop submodule. This adds a certain amount of modularization within the module itself. In a preferred embodiment, the submodules are hermaphroditic allowing two identical submodules to mate with each other or to an intermediate module and thereby further exploit modularity.
The submodules have compartments for accommodating the add/drop filters themselves. To minimize the height of the tray, the each submodule preferably uses at least two compartments thereby spreading the add/drop components horizontally. The compartments preferably are asymmetrically located such that, when the two submodules are combined, the compartments are offset from one another and do not interfere with each other. Again, this allows for a lower profile tray.
Accordingly, one aspect of the invention is a tray subassembly for use in an add/drop module. In a preferred embodiment, the tray comprises: (a) a first and second submodule, each submodule having one or more compartments for containing individual add/drop filters; (b) a first plurality of cascaded add/drop filters installed in the first submodule; and (c) a second plurality of cascaded add/drops filters installed in the second submodule.
Another aspect of the invention is an add/drop module comprising the tray. In a preferred embodiment, the module comprises: (a) a housing; (b) a tray mounted in the housing, wherein the tray comprises at least: (i) a first and second submodule, each submodule having one or more compartments for containing individual add/drop filters; (ii) a first plurality of cascaded add/drop filters installed in the first submodule; and (iii) a second plurality of cascaded add/drops filters installed in the second submodule; and (c) connectors mounted to the housing and optically connected to the fibers at the ends of the first and second plurality of cascaded add/drop filters.